1. Field of the Invention
The present invention relates to boat propellers. In another aspect, the present invention relates to boat propellers of the type having a tubular body from which propeller blades project and having an inwardly spaced hub assembly by which the propeller is attached to a propeller shaft. In still another aspect, the present invention pertains to an apparatus for the temporary or emergency enablement of such a boat propeller which has been disabled by shearing or otherwise separating of a portion of the hub assembly thereof so that the propeller body no longer rotates in response to rotation of the propeller shaft.
2. Description of the Related Art
There are many boats which are powered by outboard or inboard-outboard motors. Motors of the type in which the exhaust exists through the propeller utilize a boat propeller of the type which has a tubular body, from which propeller blades project, and an inwardly spaced hub assembly for attachment to a propeller shaft. The hub assembly typically includes an outer tubular member concentrically supported within the tubular propeller body by a plurality of radially or spirally extending ribs between which are a plurality of longitudinal spaces. The longitudinal spaces serve as exhaust ports for the motor or engine by which the propeller shaft is driven. An inner tubular sleeve of the hub assembly provides a central bore through which the propeller shaft extends for engagement by a nut or other fastener to attach the propeller to the propeller shaft.
The hub assembly may also include an intermediate tubular sleeve of resilient material concentrically fixed between the inner and outer sleeves of the hub assembly. This resilient intermediate sleeve absorbs shock and transmits power from the propeller shaft to the propeller body. However, the intermediate sleeve is assembled and is of a material such that upon application of abnormal torsional forces the intermediate sleeve is sheared or separated so that the propeller body no longer rotates in response to rotation of the shaft. Thus, the intermediate sleeve acts as a shock absorber and in severe cases shears or separates from the inner and/or outer sleeves to prevent further damage to the engine, propeller shaft or other components of the boat.
Typically, abnormal shock or torsional forces are transmitted to a propeller upon contact with a submerged obstacle, e.g., log, stump, etc. or by fouling of the propeller with seaweed, rope, etc. In the event of such an occurrence and shearing or separation of the intermediate sleeve due thereto, the propeller may be disenabled and incapable of moving the boat through the water. Such a situation could be exasperating and dangerous. If a spare propeller is not available or if the boat cannot be towed by another boat, the boat and its occupants may lie powerless for hours or days with ominous consequences.
Most boat owners and operators do not prepare for propeller disablement, thinking, as many, that this would not happen to them. Others prepare for such an event by having a spare propeller on board the boat. However, to install a spare propeller, it is necessary to remove the disabled propeller by removing a nut attached to the threaded end of the propeller shaft and pulling the inner sleeve of the propeller hub assembly off of the propeller shaft. Removing the nut is frequently the simplest part of this procedure. Disengaging the inner sleeve of the hub assembly from the propeller shaft is frequently difficult and sometimes impossible under usual circumstances. The tight fit of these members, corrosion, difficult access, lack of proper tools, etc. are all reasons why such a remedy may fail. Obviously, better and easier methods of emergency enablement of disabled boat propellers are needed and hoped for.
U.S. Pat. No. 5,071,376, issued Dec. 10, 1991 to Walker, discloses an apparatus for emergency enablement of a disabled boat propeller which includes a plate member having an aperture for engagement with and attachment to the end of the propeller shaft and further including a plurality of cantilevered members, the proximal ends of which are radially spaced from the plate member aperture. When the apparatus is attached to the end of the propeller shaft, the cantilevered members extend, parallel to the propeller shaft and the axis of the plate member aperture, projecting through longitudinal spaces between the propeller body and the hub assembly for engagement with the ribs connecting these last two members to at least temporarily restore rotational response of the propeller body to rotation of the propeller shaft.
Unfortunately, the disabled boat propeller enablement apparatus of U.S. Pat. No. 5,071,376 lacks any means for preventing damage to the engine, propeller shaft or other components of the boat, in the event that the propeller or the enablement apparatus were to encounter abnormal shock or torsional forces of the type which disabled the boat in the first instance. In such a circumstance, the boat would once again be disabled, with additional damage to the engine, propeller shaft or other components of the boat.
Boat propeller designs vary in the number and size of the exhaust ports. Thus, the disabled boat propeller enablement apparatus of U.S. Pat. No. 5,071,376, with its plurality of cantilevered members for engaging the blades of the disabled propeller, may require different designs to fit in a small three port exhaust as opposed to a large five port exhaust.